This term is not used much anymore, in part because of the ambiguity of which elements "should" be included in this category, and also because many of these "rare" elements are not especially rare.
Cerium is the 25th most abundant element in the Earth's crust, and even the least abundant of the naturally-occurring lanthanides, lutetium, the 60th most abundant element, is much more common than either silver or gold.
The period 6 inner transition metals lanthanides are cerium Ce , praseodymium Pr , neodymium Nd , promethium Pm , samarium Sm , europium Eu , gadolinium Gd , terbium Tb , dysprosium Dy , holmium Ho , erbium Er , thulium Tm , ytterbium Yb , and lutetium Lu.
The period 7 inner transition metals actinides are thorium Th , protactinium Pa , uranium U , neptunium Np , plutonium Pu , americium Am , curium Cm , berkelium Bk , californium Cf , einsteinium Es , fermium Fm , mendelevium Md , nobelium No , and lawrencium Lr. Members of the series are often called actinides, although actinium at. The series always includes the 14 elements with atomic numbers 90 through The other members are in order of increasing atomic number thorium , protactinium , uranium , neptunium , plutonium , americium , curium , berkelium , californium , einsteinium , fermium , mendelevium , nobelium , and lawrencium.
Thorium and uranium are the only actinides found in the earth's crust in appreciable quantities, although small amounts of neptunium and plutonium have been found in uranium ores. Actinium and protactinium are found in nature as decay products of some thorium and uranium isotopes.
The Actinide series contains elements with atomic numbers 89 to and is the sixth period and third group of the periodic table. The series is the row below the Lanthanide series, which is located underneath the main body of the periodic table. Both the Lanthanide and Actinide series are referred to as Rare Earth Metals and have a high diversity in oxidation numbers.
These elements, usually considered ranging from atomic number 89 to atomic number on the periodic table, have interesting properties, and play a key role in nuclear chemistry.
The modern periodic table has two rows of elements below the main body of the table. The actinides are the elements in the bottom of these two rows, while the top row is the lanthanide series.
These two rows of elements are placed below the main table because they don't fit into the design without making the table confusing and very wide. However, these two rows of elements are metals, sometimes considered a subset of the transition metals group.
In fact, the lanthanides and actinides are sometimes called the inner transition metals, referring to their properties and position on the table. Two ways of placing the lanthanides and actinides within a periodic table are including them in their corresponding rows with the transition metals, which makes the table wider, or ballooning them out, making a three-dimensional table.
There are 15 actinide elements. The electronic configurations of the actinides utilize the f sublevel, with the exception of lawrencium, a d-block element. Depending on your interpretation of the periodicity of the elements, the series begins with actinium or thorium, continuing to lawrencium. The usual list of elements in the actinide series is:. The only two actinides found in appreciable quantities in the Earth's crust are thorium and uranium. Small quantities of plutonium and neptunium are present in uranium orders.
Actinium and protactinium occur as decay products of certain thorium and uranium isotopes. The other actinides are considered synthetic elements.
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